THE INFLUENCES OF Fe(III) ION and Fe(OH) 3 COLLOID ON THE PHOTODEGRADATION of p -CHLOROPHENOL CATALYZED BY TiO 2 | Wahyuni | Indonesian Journal of Chemistry 21760 40846 1 PB

Indo. J. Chem., 2006, 6 (2), 195 - 198

195

THE INFLUENCES OF Fe(III) ION and Fe(OH)3 COLLOID ON
THE PHOTODEGRADATION of p-CHLOROPHENOL CATALYZED BY TiO2
Endang Tri Wahyuni *, Mudasir and Ngatidjo Hadipranoto
Department of Chemistry, Faculty of Mathematics and Natural Sciences,
Gadjah Mada University, Sekip Utara Yogyakarta, Indonesia 55281
Received 9 March 2006; Accepted 27 May 2006

ABSTRACT
The influences of ionic Fe(III) and colloidal Fe(OH)3 on the effectiveness of p-chlorophenol photodegradation
catalyzed by TiO2 has been studied. Photodegradation was carried out in a batch system by irradiating a suspension
of TiO2, p-chlorophenol, and Fe(III) as ionic or colloidal forms, using UV lamp for a period of time accompanied by
magnetic stirring. Concentration of photodegraded p-chlorophenol was calculated by subtracting the initial
concentration with that of undegraded p-chlorophenol. Concentration of undegraded p-chlorophenol was determined
by gas chromatography. In this study, TiO2 mass and the photodegradation time were optimized. The influences of
concentration of Fe(III) solution, mass of Fe(OH)3, and pH of the solution have also been systematically studied. The
research results showed that the presence of Fe(III) ions improved the effectiveness of photocatalytical degradation
of p-chlorophenol, which was proportional to the concentrations of Fe(III) ion. In contrast, the increasing mass of

Fe(OH)3 led to a decrease in the degree of p-chlorophenol photodegradation. Furthermore, it was observed that
increasing pH of the solution resulted in a decrease in the photodegradation of p-chlorophenol. This phenomena
may be due to the different species of TiO2 available at the surface of photocatalyst and of ionic Fe(III) and colloidal
Fe(OH)3 in the solution resulted from the pH alteration. The highest photodegradation degree, ca. 80 % was
obtained when 20 mg of TiO2 was applied in the photodegradation of 50 mL of 100 ppm p-chlorophenol solution in
3+
the presence of 100 ppm Fe irradiated by UV-light for 25 hours.
Keywords: p-chlorophenol photodegradation, TiO2, Fe(III) species
INTRODUCTION

EXPERIMENTAL SECTION

p-Chlorophenol is one of persistent hazardous
pollutants which may be delivered by several industrial
and hospital wastewaters into the environment. This
organic pollutant possesses high toxic potentials and
carcinogenic at low concentration level. Due to its
toxicity, several removal methods have been developed
including adsorption [1,2], biodegradation [3,4], and
photocatalysis degradation [5-7].

The mentioned
methods have both advantages and disadvantages.
Among the methods, photocatalysis degradation using
TiO2 semiconductor has received much attention due to
its effectiveness for p-chlorophenol removal [8-11].
In the environment, p-chlorophenol can be found
along with metal ions such as iron (Fe) and Fe(OH)3
colloid which are resulted from electroplating, painting
and other industrial wastewater. It has been reported
[12] that the presence of Fe(III) ions can significantly
improve the effectiveness of the photodegradation of pchlorophenol catalyzed by TiO2. However, the effect of
colloidal Fe(OH)3 on the photocatalysis degradation of
p-chlorophenol, so far, has not been explored yet. The
aims of the present study is to evaluate the influence of
ionic Fe(III) and and colloidal Fe(OH)3 on
the
photodegradation of p-chlorophenol catalyzed by TiO2.

Materials
p-Chlorophenol, Fe(NO3)3, Degusa Type of TiO2,

HCl and NH4OH in analytical grade were purchased
from E.Merck. Distilled water for solution preparation
and any dilution was made by Laboratory of Analytical
Chemistry, Chemistry Department, Gadjah Mada
University. Other solvents were reagent grade and
used as received.

* Corresponding author. Phone/fax : 0062-274-545188
Email address : endtw@yahoo.com (E.T. Wahyuni)

Endang Tri Wahyuni, et al.

Photocatalysis process
Photocatalysis degradation of p-chlorophenol was
conducted in batch system in a close reactor equipped
with UV lamp, as shown by Figure 1. This reaction was
carried out by irradiating a solution containing a mixture
of p-chlorophenol, ionic Fe(III) or colloidal Fe(OH)3, and
TiO2 powder,
using UV light accompanied by

magnetical stirring for a certain period of time. In
principle, the volume of reaction mixture was 100 ml
containing various concentrations of ionic Fe(III) or
various mass of colloidal Fe(OH)3, 100ppm p-chloro
phenol and various mass of TiO2. The concentration of
undegraded p-chlorophenol was determined by Gas
Chromatography.
The degree of p-chlorophenol photodegradation
was calculated by the difference between the initial and

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Indo. J. Chem., 2006, 6 (2), 195 - 198

Fig 1. Photocatalysis reactor
the residual concentrations. Hence, in this study, TiO2
mass and the photodegradation time were optimized and
the influences of concentration of Fe(III) solution, mass
of Fe(OH)3, and pH of the reaction solution was also
systematically studied.

Fig 2. The effect of TiO2 photocatalyst on the
photodegradation of p-chlorophenol

RESULT AND DISCUSSION
The effect of the presence of TiO2 photocatalyst
The effect of the TiO2 photocatalyst addition on the
photodegradation of p-chlorophenol is shown in Fig 2.
From Fig 2, it is clearly observed that without addition of
Ti2O p-chlorophenol was able to be degraded by
light/photon but the portion of degraded p-chlorophenol
reaches only around 20 % relative to initial
concentration. Interestingly, as can be seen from Fig 2,
the degree of photodegradation can be improved
significantly by the addition of TiO2 semiconductor due to
the photo-catalytical effect. Photodegradation of pchlorophenol could occur in the UV-irradiated solution
because of the production of OH radicals from water
molecules as the solution is irradiated. This mechanism
is well described by the following reaction [13]:
+

.
H2O + hv  H + OH + e
(1)
In the suspension reaction, TiO2 photocatalyst normally
exists in the form of TiOH and it would produce OH
radicals when the species is irradiated with UV light, as
presented by reactions (2) and (3), respectively.
+
TiOH + hv  > TiOH (h + e )
(2)
+
.
TiOH + h  TiOH
(3)
Therefore, two sources of OH radical generation are
available in the solution when the solution is irradiated
by UV-light, i.e.: water molecules and TiO2
photocatalyst. As a result, a larger number of OH
radicals can be obtained in the solution during UVirradiation, resulting in the higher effectiveness for the
photodegradation of p-chlorophenol in the presence of

TiO2 catalyst.
The influence of the mass of TiO2 photocatalyst
It has been demonstrated in the previous section
that the presence of TiO2 photocatalyst in the reaction

Endang Tri Wahyuni, et al.

Fig 3. The influence of TiO2 mass on the photo
degradation
mixture enhances photodegradation of p-chlorophenol
by providing OH radicals. In order to optimize the
photodegradation process, the influence of TiO2 mass
on the photodegradation process has also been
evaluated and the results are presented in Fig 3.
Fig 3 shows that improvement of the
effectiveness of the photodegradation is observed
when the mass of TiO2 is increased up to 20 mg, but
further increase in the mass of photocatalyst gives no
significant
effect

on
the
photodegradation
effectiveness. The increasing amount of TiO2 in the
solution provides much more OH radical supplies,
resulting
in
the
higher
effectiveness
of
photodegradation. However, at higher mass of TiO2,
the turbidity of the solution also increases. This gives
rise to the reduction in UV-light absorption by substrate
and/or photocatalyst, resulting in the decrease in OH
radical production and thus also decreases the
photodegradation effectiveness.
The influence of Fe(III) concentration in the
solution
The effect of Fe(III) concentration in the solution

on the photodegradation effectiveness of pchlorophenol is presented in Fig 4. It is clearly shown
that the effectiveness of the photodegradation
increases with the increasing concentration of Fe(III)
ion in the solution. This tendency may be explained
with respect to the ability of Fe(III) ions to form

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Indo. J. Chem., 2006, 6 (2), 195 - 198

Fig 4. The influence of Fe(III) concentration in the
solution
on the effectiveness of p-chlorophenol
photodegradation

Fig 6. The influence
photodegradation
3+

of

solution

pH

on

the

-

Fe OH complex in the solution which in turn will
release OH radicals in to the solution as the species
absorbs the light of suitable energy when it is irradiated
3+
[14]. Moreover, Fe OH complex is also able to capture
photogenerated electrons (represented by Equation 4),
2+
yielding a reduced form of Fe OH complex.
3+

2+
Fe OH + e  Fe OH
(4)
This capturing electron can prevent the recombination
.
process of OH radicals with free electron, e.g.: OH + e
[15], leading to the enhancement of the effectiveness of
the photodegradation. Such ability of Fe(III) ions to do so
is termed as a sensitizing effect [15]. Increasing the
concentration of Fe(III) ions in the solution gives rise to
the increase in sensitizing effect and therefore
enhancing the photodegradation process.
The influence of the mass of Fe(OH)3 colloid
Fig 5 exhibits the influence of the mass of
Fe(OH)3 colloid on the photodegradation of pchlorophenol. The figure shows a decrease in the pchlorophenol photodegradation when Fe(OH)3 colloid
was present, and the photodegradation further reduced
as the increasing mass of Fe(OH)3 colloid. It is implied
that sensitizing effect was not shown by Fe(OH)3 colloid
or event the colloid may hindrance or block the
entering light into the solution. The higher mass of
Fe(OH)3 colloid led to an increase in the light blocking
due to higher turbidity.

Endang Tri Wahyuni, et al.

Fig 5. The influence of the mass of Fe(OH)3 colloid on
the photodegradation
The influence of solution pH on the photodegradation
The influence of solution pH on the
photodegradation of p-chlorophenol in the presence of
3+
Fe ions together with that in the presence of Fe(OH)3
colloid is presented in Fig 6. Both curves exhibits the
same trend and the most effective photodegradation
was obtained at pH 1. Increasing the pH the solution
results in the decrease in the photodegradation. This
phenomena is readily understood from the viewpoint of
the speciation of p-chlorophenol, TiO2 surface, as well
as ionic Fe(III).
During the course of the photodegradation, when
p-chlorophenol is attacked by OH radical, Cl substituent
in p-cholorophenol is replaced by OH radical to yield
hydroquinone radical and which subsequently
degraded into more simple species and Cl ion. This
+
leaving group of Cl then easily combines with H ions
to form HCl [13], as described by Equation (5). This is
+
the reason why at low pH (higher concentration of H )
the effectiveness of the photodegradation is enhanced.
In contrast when the pH of the solution is increased
+
(lower concentration of H ions), as would be expected,
the effectiveness of the photodegradation of
pchlorophenol significantly decreases.
OH

OH

OH

+ Cl

Cl + H  HCl
(5)
It is important to note that at a very low pH of the
+
solution, a mixture of >TiOH2 and >TiOH were formed
at the surface of photocatalyst in which the portion of
the former species is dominant as compared to the
+
latter one [15]. Since >TiOH2 species is less effective
in providing OH ion, consequently there is fewer
radicals available in the solution. Nevertheless, at low
pH (ca.1.0) OH radical is a strong oxidizing agent [10].
Therefore, although the number of OH radicals
available in the solution is fewer, its effectiveness in
initiating degradation is not significantly affected. On
-

+

Cl

OH

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Indo. J. Chem., 2006, 6 (2), 195 - 198

the other hand, n the pH range of 2-8, >TiOH at the
surface of photocatalyst which easily release OH radical
would be the major species. In this range of pH, the
large number of photogenerated charge carriers, such
as OH radical could be generated, but their ability as
oxidizing agent is much lower. This brings about to the
decrease in the photodegradation. At pH higher than 8,
>TiO is the predominat species at the surface of
photocatalyst. This species is considered to be difficult to
release OH radical and electron into the solution thus
producing only a small number of the charge carriers, as
a result, much lower photodegradation is obtained.
From this results, it is obvious that the speciation of TiO2
resulted from pH alteration determine the effectiveness
of photodegradation as can be shown in Fig 6.
Furthermore, it has been discussed in succeeding
3+
section that the role of Fe ion in the enhancement of pchlorophenol degradation is by taking part in supplying
OH radicals and preventing recombination of electron
3+
and OH radicals simultaneously. The ionic Fe can be
found only at very low pH and it will completely
precipitate in the form of Fe(OH)3 colloid as the pH of
the solution rises in the range of 4-8. when the pH of the
solution is continuously increased to reach the level of 83+
14, Fe would partially dissolve again to form anionic
=
complexes of Fe(OH)4 and Fe(OH)5 [16]. The formed
colloids of iron could reduce the light absorption by the
species involved in reaction system, leading to less
effective photodegradation. In addition, the dissolved
=
Fe(OH)4 and Fe(OH)5 species are unlikely to release
OH radicals, therefore it is not surprising to observe low
photodegradation at high pH. In the case of pchlorophenol photodegradation in the presence of
Fe(OH)3, the similar explanation may be applied
because, more or less, the speciation of Fe(OH)3 is
3+
same as that of Fe described above. As a conclusion,
it has been proved that the changes in speciation form of
p-chlorophenol, TiO2 and Fe(III) ( as cation and colloid)
due to pH alteration control the effectiveness of the
photodegradation process and explain clearly why the
effective photodegradation is reached at relatively low
pH of the solution.
CONCLUSION
The
effectiveness
of
p-chlorophenol
photocatalytical degradation is enhanced in the
3+
presence of increasing concentration of Fe . On the
other hand, increasing mass of Fe(OH)3 colloid leads to
a decrease in the effectiveness of p-chlorophenol
photodegradation. The decline in p-chlorophenol
photodegradation is observed as the pH of the solution
is increased. However, at pH = 6, i.e.: the most
applicable pH in real waste water treatment, an
adequate effectiveness of photodegradation is still
obtained. The highest photodegradation degree, ca. 80
% is achieved when 20 mg of TiO2 is applied for the

Endang Tri Wahyuni, et al.

degradation of 50 ml of 100 ppm p-chlorophenol in the
3+
presence of 100 ppm
Fe in the solution with
irradiation time of 25 h.
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